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From "Honton, Charles" <>
Subject Re: [pool] equal instances
Date Sat, 11 Jun 2011 11:26:08 GMT
Please look at java.util.IdentityHashMap again.  I think it does
everything you're looking for except concurrent access.  Given other
requirements, I'm not sure a ConcurrentHashMap will buy much performance


On 6/11/11 5:54 AM, "Mark Thomas" <> wrote:

>On 11/06/2011 08:44, Phil Steitz wrote:
>> I have looked at this some more and I think we have two choices,
>> depending on how much we want to be able to do in terms of
>> monitoring and instance management.  The simplest solution is to
>> enable only holding references to instances checked out to clients,
>> but no tracking of last active times, etc. by the pool itself
>> (leaving this to the pooled objects themselves, as
>> AbandonedObjectPool does now).  That could be done with less
>> ambitious _allObjects and PoolableObject classes.  Actually,
>> _allObjects would go away, replaced by a List of _circulatingObjects
>> (like AbandonedObjectPool trace) and PoolableObject would really
>> only maintain state for idle instances or instances undergoing
>> lifecycle transitions.
>The problem with a List and objects where A.equals(B) is that we'll have
>to iterate through the list testing objects for equality when an object
>is returned in order to remove the right object. That will be slow. (If
>we want to prevent the same object being returned multiple times).
>> If we want to be able to track things like last active time (as the
>> trunk code now enables), we need to be able to identify returning
>> objects uniquely.  That means either we impose the factory
>> discernibility requirement or use system identity hashcodes.
>> I would like to keep the monitoring / management options open, so my
>> vote is for the second option.  I wonder, though, if it makes sense
>> to keep the base implementation simple (and a little faster) and
>> restrictive and provide the equals-tolerant functionality in a
>> subclass or via a config option.
>I too think that the second option is the way to go using system
>identity hashcodes. I'm not sure that the first option will be faster
>since iterating through the List of circulating objects is likely to be
>slower than generating a system identity hashcode and doing a lookup in
>a Map. If testing pool2/dbcp2 shows that the system identity hashcode
>makes it significantly slower than Tomcat's jdbc-pool then we can look
>at this again.
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